1. Field of the Invention
This invention relates generally to the field of dentistry and more particularly to endodontic instruments used for cleaning and enlarging a root canal of a tooth. The files of this invention are particularly well-suited for rotation first in one direction through a given arc and then rotation in a reverse direction through a reduced arc.
2. Description of the Related Art
A key procedure in endodontic therapy of treating an infected tooth is cleaning and enlarging the root canal of the tooth prior to filling with an inert obturating material such as gutta percha. Successful removal of infected tissue from the tooth greatly improves the likelihood that a patient will retain the tooth. Two alternate, primary methods have been used in cleaning and enlarging the root canal: step-back preparation and crown-down preparation. Both methods require substantial skill and time to perform properly, and each generally employs a series of three to five endodontic files that are manually rotated and advanced into the canal to clean canal surfaces and eject the debridement material from the canal for removal. Step-back preparation first employs a small instrument to the apex of the canal and then employs larger instruments for enlargement of the apex. Additional larger instruments are then applied slightly short of the apex to back out of the canal and create a taper. Crown-down preparation first employs a large instrument at the orifice of the canal. The instrument is worked apically until reaching resistance. Smaller instruments are then applied in proceeding down the canal.
Employing a handpiece to mechanically duplicate the hand techniques associated with these methods, including rotating a file, provides a beneficial improvement in efficiency. In the past, this efficiency improvement would often come at the expense of the clinician losing tactile feedback and, therefore, control of the procedure. Although the rotary handpiece has been greatly improved—see my U.S. Pat. No. 6,293,795—rotary files have not kept pace with changes in clinical practice.
Clinicians are increasingly being encourages to employ instruments as single use for safety and health reasons, however endodontic instruments are commonly employed in packages in four or more of a single size. In contrast, in a single use system the clinician first selects a small exploring file to establish a guide path to the apex and determine a working length of the canal. The clinician then selects a single working file having the desired apical size and taper to prepare the entire canal from orifice to apex. Thus a single use system can employ a package of two or three instruments, that is, an exploring file and one or two working files, all of which are used for only one patient and then the instruments are discarded.